Printed circuits containing one or more circuitry innerlayers are in prominent use today as demand increases for weight and space conservation in electronic devices.
In the typical fabrication of a multilayer printed circuit, patterned circuitry innerlayers are first prepared by a process in which a copper foil-clad dielectric substrate material is patterned with resist in the positive image of the desired circuitry pattern, followed by etching away of the exposed copper. Upon removal of the resist, the desired copper circuitry pattern remains thereon.
A composite of alternating circuitry inner layers and dielectric substrate materials is formed by interposing one or more partially-cured dielectric substrate material layers (so-called “pre-preg” layers) between the circuitry innerlayers. The composite is then subjected to heat and pressure to cure the partially-cured substrate material and achieve bonding of circuitry innerlayers. The cured composite may then have through-holes drilled therethrough, which are metallized to provide a means for conductively interconnecting all of the circuitry layers. In the course of the through-hole metallizing process, desired circuitry patterns may also be formed on the outer-facing layers of the multilayer composite.
It has long been known that the strength of the adhesive bond formed between the copper metal of the circuitry innerlayers and the cured pre-preg layers, or other non-conductive coatings, in contact therewith leaves something to be desired, with the result that the cured multi-layer composite or the coating is susceptible to delamination in subsequent processing and/or use. In response to this problem, the industry has developed the technique of forming on the copper surfaces of the circuitry innerlayers (before assembling them with pre-preg layers into a multi-layer composite) a layer of copper oxide, such as by chemical oxidation of the copper surfaces. Various approaches have been proposed for minimizing the delamination problems, some of which are described in U.S. Pat. No. 6,146,701 to Ferrier, the subject matter of which is herein incorporated by reference in its entirety.
In addition, other efforts for treating metal surfaces have utilized a so-called microetching composition, as described for example in U.S. Pat. No. 5,965,036 to Maki et al., the subject matter of which is herein incorporated by reference in its entirety. In this instance, the microetching agent comprising a small amount of a polymer compound which contains polyamine chains or a cationic group, or both, to produce a deep irregularly etched surface on the surface of copper or a copper alloy surface.
The present invention proposes a novel polymer formed from a reaction product of polyethylenimine and acrylonitrile and is usable in different compositions to improve the adhesion of polymeric materials to metal surfaces, especially copper and copper alloy surfaces during the manufacture of multi-layer printed circuit boards. Thus, the process of the invention is particularly useful in the production of multi-layer printed circuits. The process proposed herein provides optimum adhesion between the metallic and polymeric surfaces (i.e., the circuitry and the intermediate insulating layer).
The inventors of the present invention have determined that poly(ethyleneamino propionitrile) polymer, which is a reaction product comprised of polyethylenimine and acrylonitrile can beneficially be added to compositions used for roughening metal surfaces and provide improved adhesion of the metal surface to a polymeric substrate as compared with compositions of the prior art.